1. Technical Field
The present invention relates to a current measurement device and a current measurement method for measuring current that flows in a composite material containing conductive fibers.
2. Related Art
Lightning strike countermeasures for preventing the occurrence of, for instance ignition of fuel caused by sparks derived from a lightning strike, are a necessary feature in the design of aircraft airframes. Elucidation of the distribution of current in the airframe during a lightning strike is an important issue to be addressed when devising such lightning strike countermeasures. In particular, there is a demand for detailed elucidation of current distributions in composite materials such as carbon-fiber reinforced plastic (CFRP), the usage whereof in airframes has been growing in recent years.
However, currents flowing in composite materials differ from currents that flow in a metallic material. In the former case, currents are distributed in a complex manner due to, for instance, the influence of the plurality of fiber directions. Accordingly, techniques are required that allow measuring, more accurately, the currents that flow in the fibers of a composite material, in order to elucidate the current distributions in the material.
Rogowski coils or magnetic sensors are ordinarily used for current measurement. A Rogowski coil is a ring-like coil that is capable of measuring large currents. Current can be measured herein on the basis of voltage induced between both ends of the coil, by arranging the latter so as to surround a measurement site. A magnetic sensor detects magnetic fields at the measurement-site surface, such that currents can be measured on the basis of these magnetic fields (refer to, for instance, Yoichiro Tsumura, Tatsufumi Aoi, Hideo Yamakoshi, Koji Satake, Kazuo Yamamoto, “Surface magnetic field measurements using ferrite-core sensors”, ICOLSE 2009, Sep. 15, 2009)
However, current measurement relying on Rogowski coils and magnetic sensors is not suited, in view of the points below, for the measurement of currents that flow in fibers of a composite material. Measurements using Rogowski coils require the coils to be disposed surrounding fibers in a composite material, and, accordingly, holes must be opened in the composite material itself. A concern arises thereupon in that the holes may exert an influence on the current distribution. Measurements relying on magnetic sensors do not require opening of holes in the composite material; however, accurate current distributions cannot be grasped unless extremely small magnetic sensors are used, since the flow of current around fibers changes within distances in the order of several mm. Such small magnetic sensors are readily susceptible to noise, and are difficult to produce in the first place.